"Contrary to muscle and bone tissue, which get mechanically weaker with disuse, fat depots in fat cells expanded when they experienced sustained loading by as much as 50 percent. This was a substantial discovery."

The effect was contagious too — the surrounding cells started expanding too.

"This proves that you're not just what you eat. You're also what you feel — and what you're feeling is the pressure of increased weight and the sustained loading in the tissues of the buttocks of the couch potato," Professor Gefen said.

Greg Stark, trainer and founder of Better Being, says sitting all day also decreases the body's enzymes that are responsible for fat metabolism.

"The enzymes decrease by as much as 90 percent," he told ninemsn Coach.

But it's not just the fat cells expansion affecting sedentary people's butt perkiness — the muscles also waste away if they're not constantly being used.

"When it comes to the muscle side of things, it's very much the premise, 'Use it or lose it'," Stark says.

"If you are sitting, those muscles aren't being worked and the muscle will shrink and atrophy."

Of course, we're not all going to be naturally bootylicious — genetics do play a role in the size and shape of our butt. But Stark says that if you sit around most of the day your chances of having a shapely derriere sharply decline.

"But just because your family is a certain shape doesn't leave you predestined to be that shape. There are always things you can do to improve on that.

"One of the best things you can do for your butt is maximise your movement throughout the day.

"People often think that I can sit all day as long as I go to the gym but the research is showing that people's risk of disability and injury doubles with every hour they spend sitting over five hours a day, even if they exercise intensely on a regular basis," Stark explains.

"Make sure you're not in the mindset that you can sit all day as long as you are exercising because it doesn't quite work that way."

Butt-shaping workout

You can further increase your chances of a perky bottom with Stark's favourite bun exercises.

Do three sets of 30 seconds on then 30 seconds off, doing as many repetitions as you can in that 30-second period.

Walking lunges: Take a long stride forward so that your whole front foot remains flat on the floor and you are on the toes of your rear foot. Bring your rear foot forward in a walking motion and advance to the next lunge. You should feel your front leg doing all the work.

Ice skaters: Stand on one leg, bending your knee and hip, keeping your centre of gravity low. Jump to the side landing in the same position. To increase demand, reach down low with the opposite hand to the leg you are standing on.

Glute bridges: Lie on your back, with your legs bent and your feet flat on the floor. Push your hips up towards the ceiling and lower yourself down to lightly touch the floor. You can do this exercise one leg at a time to increase the demand.